The purpose of this study is to determine if the normal decline in pulmonary function with aging imposes mechanical limitations to ventilation during physical performance in healthy nonsmoking elderly men and women. The specific aims of the research are: 1. To determine if ventilation during maximal exercise is mechanically limited in elderly men and women. We hypothesize that the normal decline in maximal expiratory flow and the age-related changes in lung volumes will impose mechanical constraints to ventilation which will be evidenced by marked expiratory airflow limitation and by a minimal increase in maximal ventilation, as compared to younger subjects, when ventilatory demand is augmented during exercise by breathing a gas mixture with 3% CO2, 21% O2, and 76% N2. These studies will also address the consequence of augmented ventilatory demand on exercise capacity in the elderly. 2. To determine if the normal decline in pulmonary function with aging affects end-expiratory lung volume during exercise. We hypothesize that aging will impose mechanical constraints to ventilation which will result in an increased end-expiratory lung volume during exercise. Furthermore, we propose that the increase in end-expiratory lung volume during exercise will be associated with expiratory airflow limitation, will occur at lower levels of exercise when ventilation is augmented by breathing a gas mixture of 3% CO2, 21% O2, and 76% N2, and will be associated with the age-related decline in maximal exercise capacity. We propose to test these hypotheses by determining maximal ventilation, dynamic flow-volume and pressure-volume loops, breathing pattern, lung volumes, gas exchange, and exercise capacity when breathing room air and when breathing a gas mixture with 3% CO2, 21% O2, and 76% N2 during cycle ergometry. We will study 21 men and 16 women in each of two age-groups: 35-45 and 65-75 yr. Static lung mechanics, maximal flow-volume loops, and isovolume pressure flow curves will be measured at rest to determine age related changes in respiratory mechanics that could mechanically compromise pulmonary function during exercise.